<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <div id="box"> hello div</div>

  <script>
    // const box = {};
    HTMLElement.prototype.eat = function () {
      console.log('true');
    }
    const box = document.getElementById('box');
    box.username = 'jack';
    box.info = {
      size: 100,
      width: 200,
    }
    box.say = function () {
      console.log('hello');
    }
    box.eat();
  </script>
</body>

</html>